Ms Fernandes also said while she initially "would have liked to have taken all my crockery and broken it on his head" when he admitted his infidelity to her, she didn't want to be held down by bitterness and anger.
Mr Vaz, 59, who has two children with Ms Fernandes, quit as chairman of the influential House of Commons Home Affairs Committee after becoming embroiled in the scandal.
Ms Fernandes told the Mail on Sunday the revelation that her husband of 23 years paid two male prostitutes for sex had come "out of the blue" and was a "complete shock".
She said the Leicester East MP begged for forgiveness, saying he was "very sorry" and promising it would "never happen again" after he broke the news to her before the scandal was reported in the press.
The lawyer told the paper: "I've decided to forgive him. That's different to forgiving him right now. If I don't forgive him eventually, it is going to tear me up. It's going to destroy me and I don't want that. I don't like that feeling of anger and bitterness.
"Although I'm a lapsed Christian, there is still a Christian part of me that talks about forgiveness because you let go if you forgive. So from that point of view, yes, I've made the decision but how it will be done ... that's all to happen in the future."
"Keith is not a bad person, he's just done a terrible thing. It's absolutely terrible because it's affected all of us, because it's affected the kids.
"But he's a good person, a good father, he's been a good husband and nine-tenths of the time he's got things right. This time he's fallen... badly."
The couple will be going to marriage guidance sessions.
